Barium and strontium can substitute for calcium in stimulating nitric oxide production in the endothelium of canine coronary arteries

Are Hair Scalp Trace Elements Correlated with Atherosclerosis Location in Coronary Artery Disease?

Coronary artery disease is among the leading current epidemiological challenges. The genetic, clinical, and lifestyle-related risk factors are well documented. The reason for specific epicardial artery locations remains unsolved. The coronary artery topography and blood flow characteristics may induce local inflammatory activation. The atherosclerotic plaque formation is believed to represent inflammatory response involving enzymatic processes co-factored by trace elements. The possible relation between trace elements and coronary artery disease location was the subject of the study. There were 175 patients (107 (61) men and 68 (39) females) in a median (Q1-3) age of 71 years (65-76) admitted for coronary angiography due to chronic coronary syndrome. The angiographic results focused on the percentage of lumen stenosis in certain arteries and were compared with the results for hair scalp trace elements. The correlation between left main coronary artery atherosclerotic plaques and nickel (Ni), zinc (Zn), and antimony (Sb) hair scalp concentration was noted. The analysis revealed a positive relation between left descending artery disease and chromium (Cr), sodium (Na), arsenic (As), and molybdenum (Mo) and a negative correlation with strontium (Sr). The atherosclerotic lesion in the circumflex artery revealed correlations in our analysis with sodium (Na), potassium (K), chromium (Cr), nickel (Ni), arsenic (As), and negative with strontium (Sr) (r) hair scalp concentrations. The negative correlations between right coronary artery disease and magnesium (Mg) and strontium (Sr) concentrations were noted. The possible explanation of different epicardial artery involvement and severity by atherosclerotic processes may lay in their topography and blood rheological characteristics that induce different inflammatory reactions co0factored by specific trace elements. The trace element concentration in the hair scalp may correlate with a particular coronary atherosclerotic involvement, including the severity of lumen reduction. This may indicate the missing link between the pathophysiological processes of atherosclerosis development and its location in coronary arteries.

Inhibition of the epithelial sodium channel (ENaC) by connexin 30 involves stimulation of clathrin-mediated endocytosis

Mice lacking connexin 30 (Cx30) display increased epithelial sodium channel (ENaC) activity in the distal nephron and develop salt-sensitive hypertension. This indicates a functional link between Cx30 and ENaC, which remains incompletely understood. Here, we explore the effect of Cx30 on ENaC function using the Xenopus laevis oocyte expression system. Coexpression of human Cx30 with human αβγENaC significantly reduced ENaC-mediated whole-cell currents. The size of the inhibitory effect on ENaC depended on the expression level of Cx30 and required Cx30 ion channel activity. ENaC inhibition by Cx30 was mainly due to reduced cell surface ENaC expression resulting from enhanced ENaC retrieval without discernible effects on proteolytic channel activation and single-channel properties. ENaC retrieval from the cell surface involves the interaction of the ubiquitin ligase Nedd4-2 with PPPxY-motifs in the C-termini of ENaC. Truncating the C- termini of β- or γENaC significantly reduced the inhibitory effect of Cx30 on ENaC. In contrast, mutating the prolines belonging to the PPPxY-motif in γENaC or coexpressing a dominant-negative Xenopus Nedd4 (xNedd4-CS) did not significantly alter ENaC inhibition by Cx30. Importantly, the inhibitory effect of Cx30 on ENaC was significantly reduced by Pitstop-2, an inhibitor of clathrin-mediated endocytosis, or by mutating putative clathrin adaptor protein 2 (AP-2) recognition motifs (YxxФ) in the C termini of β- or γ-ENaC. In conclusion, our findings suggest that Cx30 inhibits ENaC by promoting channel retrieval from the plasma membrane via clathrin-dependent endocytosis. Lack of this inhibition may contribute to increased ENaC activity and salt-sensitive hypertension in mice with Cx30 deficiency.

The activation of neuronal nitric-oxide synthase by various divalent cations

Nitric-oxide synthase (NOS; EC 1.14.13.39) catalyzes the oxidation of L-arginine to nitric oxide (NO(.)) and L-citrulline via the intermediate N(omega)-hydroxy-L-arginine. Of the three distinct isoforms of NOS that have been characterized, the constitutive neuronal NOS (NOS I) generates NO(.) associated with long-term potentiation (LTP) and early brain development. All of the NOS isoforms contain an N-terminal oxidase and a C-terminal reductase domain connected by a Ca(2+)/calmodulin binding region. To activate NOS I, Ca(2+) has to bind to calmodulin, allowing electron transport through both domains. Calcium ions are tightly regulated in cells. However, a number of other metal ions that bind and activate calmodulin may also activate NOS I. One such metal ion may be Pb(2+), which is associated with neurobehavioral and psychological alterations, including the inhibition of LTP. The effect of various divalent cations on NOS I activity was tested, and the results presented herein demonstrate that Pb(2+) and Sr(2+) can activate NOS I to a level similar to that found for Ca(2+). Finally, there is a synergy between Pb(2+) and Ca(2+) resulting in maximal activation of NOS I using minimal concentrations of both metal ions.

The effect of divalent cations on bovine retinal NOS activity

The divalent cation requirements of NOS activity in bovine retina homogenate supernatant were investigated. Supernatants were assayed under standard conditions (in mM: EDTA 0.45, Ca2+ 0.25, Mg2+ 4.0). In order to investigate the enzyme's dependence on divalent cations, the tissue homogenate was depleted of di- and trivalent cations by passing it over a cation-exchange column (Chelex 100). Surprisingly, NOS activity was 50-100% higher in this preparation. However, addition of either EDTA (33 microM) or EGTA (1 mM) almost fully inhibited NOS activity, suggesting a requirement for residual divalent metal cation(s). Phenanthroline or iminodiacetic acid at low concentrations had little effect on activity, suggesting no requirement for Fe2+, Zn2+ or Cu2+. Ca2+ had a moderate stimulatory effect, with an optimum activity around 0.01 mM. Mg2+ or Mn2+ had little effect at concentrations < 0.25 mM. However, in the presence of EDTA, Mn2+ or Ca2+ markedly stimulated NOS activity with the optimum at 0.1 mM. At high concentrations (> 0.1-0.2 mM), all divalent cations tested (Ba2+, Zn2+, Co2+, Mn2+, Mg2+, Ca2+), as well as La3+, dose-dependently inhibited NOS activity. We propose that retinal NOS requires low concentrations of naturally occurring divalent metal ions, most probably Ca2+, for optimal activity and is inhibited by high di- and trivalent metal concentrations, probably by competition with Ca2+.

Relative and combined effects of ethanol and protein deficiency on strontium and barium bone content and fecal and urinary excretion

Strontium metabolism has attracted considerable interest because of to its interaction with calcium, the bone alterations detected after treatment with strontium, and its potential value as a paleodietary indicator. The effects of ethanol on strontium and barium metabolism-another divalent cation which also accumulates in bone--is largely unknown. Based on this fact, we have determined bone content and fecal and urinary excretion of Ba and Sr in four groups of eight animals each pair-fed for 8 wk with (1) a nutritionally adequate diet, (2) a 36% (as energy) ethanol-containing isocaloric diet, (3) a 2% protein, isocaloric diet, and (4) a 36% ethanol, 2% protein isocaloric diet, following the Lieber-DeCarli model. Five additional rats were fed with the control diet ad libitum. We have found that ethanol tends to decrease and a low protein diet to increase bone strontium content; the decrease in bone strontium in the ethanol-fed rats is accompanied by an increase in the absolute excretion of strontium in urine. Ethanol also decreases bone barium content, but the effect of ethanol on urinary barium excretion is opposite that of strontium, a decrease. Thus, we conclude that ethanol alters both barium and strontium metabolism and bone deposition.

Direct activation of endothelial NO pathway by Ba2+ in canine coronary artery

1. We have reported that Ba2+ causes endothelium-dependent relaxation of canine coronary arteries through NO synthesis in Ca2+-free and depolarizing solution. To determine the cellular mechanisms by which the endothelium-dependent relaxation occurs, we used fura-2 fluorometry (F350 and F390; excitation wavelengths, 350 and 390 nm, respectively) and estimated the intracellular Ba2+ concentration in endothelial and vascular smooth muscle cells. 2. Ba2+ (10(-3) M) increased the fura-2 ratio (F350/F390) recorded from a combined preparation of smooth muscle and endothelium (0.445+/-0.073, n = 4) and contracted the arteries in the presence of 80 mM K+ (0.22+/-0.06 g, n = 4). 3. Diltiazem (3 x l0(-6) M) blocks Ba2+ entry into vascular smooth muscle cells via L-type Ca2+ channels. In this condition, Ba2+ increased the fura-2 ratio in endothelial cells (0.141+/-0.014, n = 5) and relaxed the underlying smooth muscle (0.08+/-0.01 g, n = 5) by a mechanism which was sensitive to 10(-4) M NG-methyl-L-arginine (L-NMMA). 4. Ba2+-induced relaxation was not attenuated with repeated application and was elicited even after endothelium-dependent relaxations in response to 10(-6) M bradykinin were abolished due to tachyphylaxis. Neither 10(-2) M caffeine nor 10(-6) M thapsigargin had effect upon Ba2+-induced relaxation. 5. To further rule out changes in intracellular Ca2+ as a mechanism of Ba2+-induced relaxation, fura-2 fluorescence was measured at the isosbestic wavelengths for Ca2+ (360 nm) and Ba2+ (370 nm) in endothelium-intact arteries. Ba2+ altered F360, but not F370, suggesting little or no contribution of intracellular Ca2+ to the phenomenon of Ba2+-induced relaxation. 6. These results suggest that the Ba2+-induced relaxation is due to its direct activation of endothelial NO synthesis without mobilization of intracellular Ca2+.

Modulatory role of endothelial calcium level in vascular tension of canine depolarized coronary arteries

The vascular tension in the coronary artery is modulated by factors released by endothelial cells. We investigated the relationship between the Ca2+ level in endothelium and endothelium-mediated changes in smooth muscle tone in high K(+)-depolarized canine coronary arteries by measuring intracellular Ca2+ concentration fluorimetrically with the Ca2+ indicator fura 2. Addition of Ca2+ (1 mM) caused an increase in endothelial Ca2+ and relaxed the 30 mM K(+)-depolarized arteries following inhibition of Ca2+ influx in the smooth muscle with diltiazem. This relaxation was inhibited by NG-monomethyl-L-arginine. As extracellular K+ concentration was decreased, increases of endothelial Ca2+ were augmented, whereas the relaxation was decreased. Basal muscle tone was found to be decreased in low K+ by measuring relaxation by sodium nitroprusside. These results suggest the importance of Ca2+ level in the endothelium in playing a modulatory role in coronary tension through the production of nitric oxide. The correlation of extracellular K+ to Ca2+ level in the endothelium indicates a typical characteristic of the passive Ca2+ entry pathway in the endothelium, whereas the resultant relaxation appears to be restricted by the basal muscle tone.

Barium activates rat cerebellar nitric oxide synthase

Ba2+ is known to pass through N-methyl-D-aspartate receptor channels and cause an increase in cGMP levels in rat cerebella. In the present study, we compared the activation of rat cerebellar nitric oxide synthase (NOS) by Ba2+ with that produced by Ca2+. Both cations stimulated L-citrulline formation in the presence of calmodulin in identical fractions eluted from an anion exchange column with a salt gradient. EC50 values for Ca2+ and Ba2+ were 200 nM and 50 microM, respectively. The IC50 of NG-monomethyl-L-arginine was the same (200 nM). These indicate a possible action of Ba2+ on NOS through the calmodulin-dependent pathway.